The present invention relates generally to medical surgical devices, systems, and methods. More specifically, the invention relates to devices, systems and methods for enhancing knee surgery including measuring forces in flexion and/or extension gap(s) during knee arthroplasty.
The knee is generally defined as the point of articulation of the femur with the tibia. Structures that make up the knee include the distal femur, the proximal tibia, the patella, and the soft tissues within and surrounding the knee joint, the soft tissues including the ligaments of the knee. The knee is generally divided into three compartments: medial (the inside part of the knee), lateral (the outside part of the knee), and patellofemoral (the joint between the kneecap and the femur). The medial compartment comprises the medial joint surfaces of the femur, tibia, and the meniscus wedged therebetween. The lateral compartment comprises the lateral joint surfaces of the femur, tibia, and the meniscus wedged therebetween. The patellofemoral compartment comprises the joint between the undersurface of the kneecap or patella and the femur. Four ligaments are especially important in the stability, alignment and functioning of the knee—the anterior cruciate ligament, the posterior cruciate ligament, the medial collateral ligament, and the lateral collateral ligament. In an arthritic knee, protective cartilage at the point of articulation of the femur with the tibia is often worn away, allowing the femur to directly contact the tibia. This bone-on-bone contact can cause significant pain, discomfort, and disability for a patient and will often necessitate knee replacement or knee arthroplasty.
Knee arthroplasty involves replacing the diseased and painful joint surface of the knee with metal and plastic components shaped to allow natural motion of the knee. Knee replacement may be total or partial. Total knee replacement surgery, also referred to as total knee arthroplasty (“TKA”), involves a total replacement of the distal end of the femur, the proximal end of the tibia, and often the inner surface of the patella with prosthetic parts. Cuts are made on the distal end of the femur and the proximal end of the tibia. Prosthetic parts are then attached. The prosthetic parts create a stable knee joint that moves through a wide range of motion. The replacement of knee structures with prosthetic parts allows the knee to avoid bone-on-bone contact and provides smooth, well-aligned surfaces for joint movement.
In TKA, the distal end of the femur and the proximal end of the tibia are completely removed. Thus, healthy tissue may be removed as well. For patients with worn out cartilage in only one compartment, an alternative to TKA may be partial knee replacement, or unicompartmental knee arthroplasty (“UKA”), an example of which is the Oxford® Partial Knee Replacement procedure. Advantages of UKA compared to TKA include smaller incisions, easier post-op rehabilitation, shorter hospital stay, less blood loss, lower risk of infection, stiffness, and blood clots, and easier revision surgery if necessary.
A challenge in knee replacement surgeries, including both TKA and UKA, is the proper balancing of ligament tension, especially of the medial and lateral collateral ligaments, through the full range of motion of the knee, from a flexed position to a fully extended position. The collateral ligaments, which connect the distal femur and proximal tibia on the medial and lateral sides of the knee, account for much of the stability and movement of the knee. Uneven ligament tension after knee replacement surgery will typically lead to symptoms including joint instability and poor patellar tracking, limited range of motion, impaired function of the knee, and uneven, increased wear and/or loosening of the prosthetic device. These symptoms may often necessitate a repeat surgery. Thus, it is imperative for the short and long-term success of a knee replacement procedure to achieve balanced ligament tension in the knee through the full range of motion of the knee.
Balancing ligament tension during knee replacement surgery is complicated by the fact that the natural knee does not operate like a hinge moving about a single axis. The knee exhibits dynamic rotation of the tibia relative to the femur as the knee moves from its flexed position to its fully extended position and vice versa. Thus, the natural knee exhibits a rotary laxity that allows the tibia to rotate through a limited internal and external arc during knee flexion. Additionally, the femur translates anteriorly and posteriorly as the tibia is being flexed about it, bringing yet another movement variable. Thus, the ligaments of the knee, along with the femur, tibia and patella, create a dynamic bio-mechanism, making ligament tension balancing in TKA surgery challenging. Many articles and studies have been devoted to ligament tension balancing in TKA, such as: Mihalko, W. H. et al., “Comparison of Ligament-Balancing Techniques During Total Knee Arthroplasty,” Journal of Bone & Joint Surgery, Vol. 85-A, Supplement 4, 2003, 132-135; Eckhoff, D. G. et al., “Three-Dimensional Morphology and Kinematics of the Distal Part of the Femur Viewed in Virtual Reality, Journal of Bone & Joint Surgery, Vol. 85-A, Supplement 4, 2003, 97-104; and Ries, M. D., et al., “Soft-Tissue Balance in Revision Total Knee Arthroplasty,” Journal of Bone & Joint Surgery, Vol. 85-A, Supplement 4, 2003, 38-42.
One technique for balancing collateral ligament tension during a knee replacement procedure involves cutting fibers of one or both ligaments to decrease ligament tension—a technique referred to as “ligament release.” A disadvantage of this technique is that the cutting of ligament tissue weakens the ligament(s) and leaves less room for error if future ligament releases or knee replacement procedures are required.
Rather than or in addition to ligament release, the components of a knee prosthesis may be selected and positioned to balance ligament tension. In a typical knee replacement procedure, multiple cuts are made to the distal femur before attaching the femoral component of the prosthesis. Most TKA procedures, for example, involve making distal cuts across the distal end of the femur, anterior and posterior cuts, and angled anterior and posterior chamfer cuts to help secure the femoral component solidly in place. The surgeon attempts to make these femoral bone cuts to achieve a position and orientation of the femoral prosthetic component so as to optimally balance ligament tension through a full range of motion of the knee. However, it is often very challenging to position the femoral bone cuts and femoral prosthetic component to provide ideal ligament tension through the full range of motion of the knee. This is due primarily to the complexity of motion about the knee, as described above, and the difficulty of placing the femoral component so as to maintain desired ligament tension through the full range of motion.
A number of devices and techniques have been described that attempt to facilitate ligament balancing during a TKA procedure. Some techniques, such as those described in U.S. Pat. No. 5,733,292, involve trial prosthesis components which are used after femoral and tibial bone cuts are made to assess ligament tension. Some devices, such as those described in U.S. Patent Application Publication No. 2003/0187452 A1, are used to measure a gap between the distal femur and proximal tibia in extension and to help a surgeon recreate that same gap when the knee is in flexion. Other “gap checking” devices are described in U.S. Pat. No. 6,575,980. Other devices have been developed to help measure an amount of ligament tension or to apply a desired amount of tension to the ligaments. U.S. Pat. No. 4,501,266, for example, describes a knee distraction device for applying a desired amount of tension. Many paddle-like devices have been suggested for applying or measuring tension across a knee joint, such as the devices described in U.S. Pat. Nos. 5,597,379; 5,540,696; 5,800,438; 5,860,980; 5,911,723; and 6,022,377. Other methods and device are described in co-assigned and co-pending U.S. patent application Ser. Nos. 10/773,608, 10/973,936 , and Ser. No. 11/149,944 , the contents of which are fully incorporated herein by reference.
The devices described for facilitating ligament balancing during a TKA procedure may also find use in UKA procedures. In certain UKA procedures, for example, the Oxford® Partial Knee Replacement, a surgeon may be provided with a set of shims or feeler gauges, each with a certain thickness. The shims or feeler gauges are used to measure the gap between the distal femur and proximal tibia to facilitate balancing knee tension. Once a side of the distal femur and a complementary side of the proximal tibia has been cut or milled down, the surfaces of the distal femur and proximal tibia may be fitted with template prostheses. With the knee in flexion, the surgeon may measure the thickness of the gap between the femoral and tibial prostheses by placing a shim or feeler gauge into the gap so that “natural tension” in the knee is achieved. “Natural tension” may be achieved when the shim or feeler gauge slides in and out of the gap easily but does not tilt. With the shim or feeler gauge removed, the knee is then extended, for example, in 20 degrees of flexion, and the gap similarly measured. Tension in the knee can be balanced by further cutting or milling off the end of the distal femur so that the gap between the distal femur and proximal tibia is the same when the knee is in flexion as when the knee is extended. The distal femur is further cut or milled based on the difference between the gap size of the knee in flexion and the gap size of the knee extended. For example, if the flexion gap is measured to be 5 mm and the extension gap is measure to be 2 mm, the amount of bone to be milled is 3 mm. This procedure, however, is highly dependent on the subjective “feel” of the surgeon. Thus, there is a need to quantify and standardize the procedure.
For the above reasons, a need exists for improved devices, systems and methods for enhancing knee replacement surgery and specifically for dynamically balancing ligaments during knee replacement to improve range of motion, stability, and patellar tracking of the prosthetic knee joint. Ideally, such devices and methods would allow a surgeon to achieve a desired ligament tension balance before committing to and making final bone cuts to the femur. Such devices would ideally be simple to use in conjunction with existing knee replacement procedures and equipment such as prosthesis templates, measurement guides, cutting guides, and saw blades or burs. At least some of these objectives will be met by the present invention.